[iOS] Change the NTP animation to use an animator

This CL updates how the NTP animations to shift tiles up (i.e. when the
omnibox is focused), using an animator instead of the regular UIView
-animate:completion:.
It allows to stop the animation in the middle without having the
animated properties in an undefined state.

Bug: 1101331
Change-Id: Iadff66283784c7a339770b58270099678cf2616c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2278253
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784857}

ios/chrome/browser/ui/content_suggestions/content_suggestions_collection_synchronizing.h

@@ -5,6 +5,8 @@
 #ifndef IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_COLLECTION_SYNCHRONIZING_H_
 #define IOS_CHROME_BROWSER_UI_CONTENT_SUGGESTIONS_CONTENT_SUGGESTIONS_COLLECTION_SYNCHRONIZING_H_
 
+#import <UIKit/UIKit.h>
+
 #import "base/ios/block_types.h"
 
 // Synchronization protocol used by the ContentSuggestions header controller to
@@ -17,7 +19,8 @@
 // when the collection is scrolled to top. |animations| is called only if it is
 // not yet scrolled to the top.
 - (void)shiftTilesUpWithAnimations:(ProceduralBlock)animations
-                        completion:(ProceduralBlock)completion;
+                        completion:
+                            (void (^)(UIViewAnimatingPosition))completion;
 // Notifies the collection that its layout has changed and should be
 // invalidated.
 - (void)invalidateLayout;

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_synchronizer.mm

@@ -37,6 +37,8 @@ const CGFloat kShiftTilesUpAnimationDuration = 0.25;
 
 // Tap gesture recognizer when the omnibox is focused.
 @property(nonatomic, strong) UITapGestureRecognizer* tapGestureRecognizer;
+// Animator for the shiftTilesUp animation.
+@property(nonatomic, strong) UIViewPropertyAnimator* animator;
 @end
 
 @implementation ContentSuggestionsHeaderSynchronizer
@@ -81,6 +83,12 @@ initWithCollectionController:
 
   self.shouldAnimateHeader = YES;
 
+  if (self.animator.running) {
+    [self.animator stopAnimation:NO];
+    [self.animator finishAnimationAtPosition:UIViewAnimatingPositionStart];
+    self.animator = nil;
+  }
+
   if (self.collectionShiftingOffset == 0 || self.collectionView.dragging) {
     self.collectionShiftingOffset = 0;
     [self updateFakeOmniboxOnCollectionScroll];
@@ -103,7 +111,8 @@ initWithCollectionController:
 }
 
 - (void)shiftTilesUpWithAnimations:(ProceduralBlock)animations
-                        completion:(ProceduralBlock)completion {
+                        completion:
+                            (void (^)(UIViewAnimatingPosition))completion {
   // Add gesture recognizer to collection view when the omnibox is focused.
   [self.collectionView addGestureRecognizer:self.tapGestureRecognizer];
 
@@ -117,7 +126,7 @@ initWithCollectionController:
   if (self.collectionController.scrolledToTop) {
     self.shouldAnimateHeader = NO;
     if (completion)
-      completion();
+      completion(UIViewAnimatingPositionEnd);
     return;
   }
 
@@ -131,29 +140,43 @@ initWithCollectionController:
   self.collectionController.scrolledToTop = YES;
   self.shouldAnimateHeader = YES;
 
-  [UIView animateWithDuration:kShiftTilesUpAnimationDuration
-      animations:^{
-        if (self.collectionView.contentOffset.y < pinnedOffsetY) {
-          if (animations)
-            animations();
-          // Changing the contentOffset of the collection results in a scroll
-          // and a change in the constraints of the header.
-          self.collectionView.contentOffset = CGPointMake(0, pinnedOffsetY);
-          // Layout the header for the constraints to be animated.
-          [self.headerController layoutHeader];
-          [self.collectionView.collectionViewLayout invalidateLayout];
-        }
-      }
-      completion:^(BOOL finished) {
-        // Check to see if the collection are still scrolled to the top -- it's
-        // possible (and difficult) to unfocus the omnibox and initiate a
-        // -shiftTilesDown before the animation here completes.
-        if (self.collectionController.scrolledToTop) {
-          self.shouldAnimateHeader = NO;
-          if (completion)
-            completion();
-        }
-      }];
+  __weak __typeof(self) weakSelf = self;
+
+  self.animator = [[UIViewPropertyAnimator alloc]
+      initWithDuration:kShiftTilesUpAnimationDuration
+                 curve:UIViewAnimationCurveEaseInOut
+            animations:^{
+              if (!weakSelf)
+                return;
+
+              __typeof(weakSelf) strongSelf = weakSelf;
+              if (strongSelf.collectionView.contentOffset.y < pinnedOffsetY) {
+                if (animations)
+                  animations();
+                // Changing the contentOffset of the collection results in a
+                // scroll and a change in the constraints of the header.
+                strongSelf.collectionView.contentOffset =
+                    CGPointMake(0, pinnedOffsetY);
+                // Layout the header for the constraints to be animated.
+                [strongSelf.headerController layoutHeader];
+                [strongSelf.collectionView
+                        .collectionViewLayout invalidateLayout];
+              }
+            }];
+
+  [self.animator addCompletion:^(UIViewAnimatingPosition finalPosition) {
+    if (!weakSelf)
+      return;
+
+    if (finalPosition == UIViewAnimatingPositionEnd)
+      weakSelf.shouldAnimateHeader = NO;
+
+    if (completion)
+      completion(finalPosition);
+  }];
+
+  self.animator.interruptible = YES;
+  [self.animator startAnimation];
 }
 
 - (void)invalidateLayout {

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_view_controller.mm

@@ -547,17 +547,24 @@ using base::UserMetricsAction;
     };
   }
 
-  void (^completionBlock)() = ^{
-    self.headerView.omnibox.hidden = YES;
-    self.headerView.cancelButton.hidden = YES;
-    self.headerView.searchHintLabel.alpha = 1;
-    self.headerView.voiceSearchButton.alpha = 1;
-    self.disableScrollAnimation = NO;
-    [self.dispatcher fakeboxFocused];
-    if (IsSplitToolbarMode()) {
-      [self.dispatcher onFakeboxAnimationComplete];
-    }
-  };
+  void (^completionBlock)(UIViewAnimatingPosition) =
+      ^(UIViewAnimatingPosition finalPosition) {
+        self.headerView.omnibox.hidden = YES;
+        self.headerView.cancelButton.hidden = YES;
+        self.headerView.searchHintLabel.alpha = 1;
+        self.headerView.voiceSearchButton.alpha = 1;
+        self.disableScrollAnimation = NO;
+        if (finalPosition == UIViewAnimatingPositionEnd &&
+            [self.delegate isScrolledToTop]) {
+          // Check to see if the collection are still scrolled to the top --
+          // it's possible (and difficult) to unfocus the omnibox and initiate a
+          // -shiftTilesDown before the animation here completes.
+          [self.dispatcher fakeboxFocused];
+          if (IsSplitToolbarMode()) {
+            [self.dispatcher onFakeboxAnimationComplete];
+          }
+        }
+      };
 
   [self.collectionSynchronizer shiftTilesUpWithAnimations:animations
                                                completion:completionBlock];